The field of the invention generally pertains to bearings. The invention relates more particularly to a bearing having one or more layers of lubricated spacers which are positioned to slide in surface-to-surface contact between a pair of surfaces independently movable relative to each other, wherein the spacers provide for a more uniform load distribution while reducing the relative sliding velocities of the pair of surfaces.
Various types of bearings have been used to reduce and/or overcome friction, the physical phenomena which resists relative sliding motion between solid bodies. In particular, many bearing designs typically incorporate the use of ball or roller elements to reduce friction by producing a rolling effect between moving surfaces. One example of this type of bearing is shown in U.S. Pat. No. 2,782,079, disclosing a railroad coaster bearing having a plurality of concentrically layered conical roller bearings 48, 50, 56, 58, 72, 74, which rotatably support annular race members 60, 62. The annular race members are rotatably mounted between the roller bearings for free movement relative to the fixed bearing support 10 and the rotating shaft 24. Additionally, in U.S. Pat. No. 2,941,853, a thrust bearing is shown disclosing multiple ball bearings, 15, 16, 17 positioned in layers along the longitudinal axis of a rotating shaft 11 for supporting axial thrusts. Each layer of ball bearings is supported by concentric annular pistons 20, 21, 22, such that axial thrusts against the ball bearings are distributed to the annular pistons.
Perhaps the greatest disadvantage of such ball or roller bearings disclosed in patents ""079, and ""853, however, is the inadequate load distribution caused by the relatively small area of contact between the balls or rollers and the sliding surfaces, e.g. the races. Loads placed on the bearing are concentrated at the contact points such that indentations known as xe2x80x9cpits xe2x80x9d are formed on the race surface, and/or the balls or rollers themselves experience some deformation at their contact points. Typically, ball or roller bearings have limited lives that are measured by the number of revolutions that can be tolerated under a given load before the ball or roller surfaces develop xe2x80x9cpitsxe2x80x9d. Because of this limitation, ball bearings are typically not suitable for supporting heavy or impact loads.
In contrast to ball or roller-type bearings, another type of bearing known as hydrostatic bearings have been commonly used to provide uniform load distribution. In U.S. Pat. No. 4,542,994, one embodiment of a hydrostatic bearing is shown having a ring-shaped member 24 hydrostatically suspended between a housing member 1 and a rotating shaft member 2. Hydrostatic suspension is provided by two separate pressure sources: a first pressure source 29 which maintains a clearance between the ring-shaped member 24 and the surrounding channel, and a separate second pressure source 4 which maintains the clearance 9 between the shaft member 2 and a circumferential land portion 7c of the ring-shaped member 24.
While hydrostatic bearings can provide uniform support and avoid the possibility of xe2x80x9cpitting,xe2x80x9d this type of bearing requires a continuous supply of hydrostatic pressure from a pressure source. Although the use of complicated pressure delivery systems and devices may be justified for large scale, high precision applications, it is usually far too expensive for small-scale, self-contained bearing applications, such as in bicycle gears, small appliances, etc. Further, while the hydrostatic fluid suspension of a single race member can be relatively simply accommodated, the complexity and expense of multiple xe2x80x9cfloatingxe2x80x9d sleeves can far outweigh any benefits derived therefrom.
In summary, there is a need to provide a simple and cost-effective bearing capable of improving load distribution over a contact area while simultaneously reducing friction. Ideally, it would be advantageous to distribute load over an area comprising an infinite number of rollers to effect uniform load distribution and prevent pitting. However, while hydrostatic bearings are capable of providing desirable uniform load distributions, they are typically much too expensive for widespread use on more commonplace bearing applications.
It is an object of the present invention to provide a simple, cost effective, and operationally efficient bearing having one or more layers of lubricated spacers for dynamically brace-supporting a pair of surfaces independently movable relative to each other.
It is a further object of the present invention to provide a bearing capable of improved load distribution over a contact surface area to avoid pitting commonly seen with ball and roller bearings under heavy and extreme load conditions.
It is a still further object of the present invention to provide a bearing capable of low relative velocities between adjacent moving surfaces, in order to reduce friction-generated heat.
The present invention is for a bearing for dynamically brace-supporting first and second slide surfaces which are independently movable relative to each other. The bearing comprises at least one spacer layeredly positioned between the first and second slide surfaces. The spacer(s) has a pair of opposing spacer slide surfaces, and each spacer slide surface is adapted to slide in surface-to-surface contact relative to a corresponding slide surface adjacent to it. In a first preferred embodiment, the bearing includes means for reducing friction between the slide surfaces to enable low friction sliding relative to each other. In a second preferred embodiment, the spacer(s) is comprised of a solid lubricant having a low coefficient of friction to enable low friction sliding between the slide surfaces. Additionally, the present invention can be in the form of various physical embodiments which enable low friction sliding while supporting various load conditions.